using OrdinaryDiffEqLowOrderRK
using Trixi

###############################################################################
# semidiscretization of the linear advection equation

advection_velocity = (0.2, -0.7)
equations = LinearScalarAdvectionEquation2D(advection_velocity)

initial_condition = initial_condition_convergence_test

boundary_condition = BoundaryConditionDirichlet(initial_condition)
boundary_conditions = (; all = boundary_condition)

# Create DG solver with polynomial degree = 3 and (local) Lax-Friedrichs/Rusanov flux as surface flux
solver = BlockFV(n_nodes = 4, surface_flux = flux_lax_friedrichs)

# Deformed rectangle that looks like a waving flag,
# lower and upper faces are sinus curves, left and right are vertical lines.
f1(s) = SVector(-1.0, s - 1.0)
f2(s) = SVector(1.0, s + 1.0)
f3(s) = SVector(s, -1.0 + sin(0.5 * pi * s))
f4(s) = SVector(s, 1.0 + sin(0.5 * pi * s))
faces = (f1, f2, f3, f4)

Trixi.validate_faces(faces)
mapping_flag = Trixi.transfinite_mapping(faces)

# Unstructured mesh with 24 cells of the square domain [-1, 1]^n
mesh_file = Trixi.download("https://gist.githubusercontent.com/efaulhaber/63ff2ea224409e55ee8423b3a33e316a/raw/7db58af7446d1479753ae718930741c47a3b79b7/square_unstructured_2.inp",
                           joinpath(@__DIR__, "square_unstructured_2.inp"))

mesh = P4estMesh{2}(mesh_file, polydeg = 3,
                    mapping = mapping_flag,
                    initial_refinement_level = 2)

# A semidiscretization collects data structures and functions for the spatial discretization
semi = SemidiscretizationHyperbolic(mesh, equations, initial_condition, solver;
                                    boundary_conditions = boundary_conditions)

###############################################################################
# ODE solvers, callbacks etc.

# Create ODE problem with time span from 0.0 to 0.2
tspan = (0.0, 10.0)
ode = semidiscretize(semi, tspan)

# At the beginning of the main loop, the SummaryCallback prints a summary of the simulation setup
# and resets the timers
summary_callback = SummaryCallback()

# The AnalysisCallback allows to analyse the solution in regular intervals and prints the results
analysis_callback = AnalysisCallback(semi, interval = 100)

# The SaveSolutionCallback allows to save the solution to a file in regular intervals
save_solution = SaveSolutionCallback(interval = 100,
                                     solution_variables = cons2prim)

# The StepsizeCallback handles the re-calculation of the maximum Δt after each time step
stepsize_callback = StepsizeCallback(cfl = 0.7)

# Create a CallbackSet to collect all callbacks such that they can be passed to the ODE solver
callbacks = CallbackSet(summary_callback, analysis_callback, save_solution,
                        stepsize_callback)

###############################################################################
# run the simulation

# OrdinaryDiffEq's `solve` method evolves the solution in time and executes the passed callbacks
sol = solve(ode, Euler();
            dt = 1, # solve needs some value here but it will be overwritten by the stepsize_callback
            ode_default_options()..., callback = callbacks);
